幻灯片8
Unit6 Nontraditional Machining Processes ? 6.2 Electrical Discharge Machining (EDM)
Electrical discharge machining sometimes is colloquially referred to as spark machining, spark eroding, burning, die sinking or wire erosion. colloquially [k?'l?ukwi?li] adj.口语的，会话的 幻灯片9
Unit6 Nontraditional Machining Processes ? 6.2 Electrical Discharge Machining (EDM)
? The main attraction of EDM over traditional machining processes
such as metal cutting using different tool and grinding is that this technique utilizes thermoelectric process to erode undesired materials from the workpiece by a series of rapidly recurring discrete electrical sparks between workpiece and electrode. ? thermoelectric [?θ?:m?ui?lektrik] adj. 热电的 ? recurring adj. 循环的
? discrete adj.分离的，不相关联的 ? electrode n.电极
幻灯片10
Unit6 Nontraditional Machining Processes
? The main attraction of EDM over traditional machining processes such as metal cutting using different tool and grinding is that this technique utilizes thermoelectric process to erode undesired materials from the workpiece by a series of rapidly recurring discrete electrical sparks between workpiece and electrode.
相比利用不同刀具进行金属切削和磨削的常规加工而言，电火花加工的吸引人之处在于它利用工件和电极之间一系列重复产生的（脉冲）离散电火花所产生的热电作用从工件表面通过电腐蚀去除掉多余的材料。 幻灯片11
? 拓展词汇
? Mechanical properties 机械性能 ? 弹性 elasticity [?l?st?s?ti:] ? 塑性 plasticity [pl?'st?s?t?] ? 刚度 rigidity ? 强度 strength ? 硬度 hardness
? 冲击韧性 impact toughness ? 疲劳强度 fatigue strength 断裂韧性 fracture toughness 幻灯片12
Unit6 Nontraditional Machining Processes ? 6.2 Electrical Discharge Machining (EDM)
EDM removes material by discharging an electrical current, normally stored in capacitor bank, across a small gap between the tool (cathode) and the workpiece (anode) typically in the order of 50 volts/10apms. 电火花加工是利用存储在电容器组中的电能（一般在50伏/10安量级）在工具电极（阴极）和工件电极（阳极）之间的微小间隙进行放电来去除材料的加工方法。 幻灯片13
Unit6 Nontraditional Machining Processes ? 6.2 Electrical Discharge Machining (EDM)
? This cause conducting particles suspended in dielectric to concentrate at the points of strongest electrical field.
When the potential difference between the electrode and the workpiece is sufficiently high, the dielectric breaks down and a transient spark discharges through the dielectric fluid, removing small amount of material from the workpiece surface.
? 这就会使悬浮在电介质的导电粒子聚集在电场最强处。 ? 当工具电极和工件电极之间的电势差足够高时，电介质被击穿从而在电介质流体中会产生瞬时电火花，将少量材料从工件表面蚀除掉。
幻灯片14
Unit6 Nontraditional Machining Processes ? 6.2 Electrical Discharge Machining (EDM)
? The volume of the material removed per spark discharge is typically in the range of 10-5 to 10-6 mm3. The gap is only a few thousandths of an inch, which is maintained at a constant value by the servomechanism that actuates and controls the tool feed. ? thousandth ['θauz?ntθ] n. 千分之一 actuates vt. 驱使,激励
每次电火花蚀除的材料量通常都在10-5～10-6 mm3范围内。电极之间的间隙只有千分之几英寸，通过伺服机构驱动和控制工具
电极的进给使该值保持常量。 幻灯片15 Scientific notation
? 103 :ten to the power of three.
? 7.39×106 :seven point three nine times ten to the power of six. ? 82600=8.26×10×10×10×10=8.26×104
? This is an equation, which reads eighty-two thousand, six hundred equals eight point two six times ten, times ten, times ten, times ten equals eight point two six times ten to the power of four. ? 3×10-5: three times ten to the power of minus five.
? ―+‖plus ― – ‖ minus
幻灯片16